1. Field of the Invention
The present invention relates to an alternator in which air flows in stepped portions between teeth partitioning slots together with rotation of a rotor.
2. Description of the Related Art
Conventionally, alternators having a stator in which a stator winding is installed in a stator core by winding conducting wires into slots of the stator core are known, and wedges may be disposed between teeth constituting entrance portions of each of the slots to prevent the conducting wires from dislodging from the slots.
In such cases, because stepped portions arise between surfaces of the teeth and inner peripheral surfaces of the wedges, fluctuations in air density occur at the stepped portions when a rotor disposed inside the stator rotates at high speed, giving rise to resonance effects, thereby generating wind noise having components in orders dependent on the number of stator teeth (number of slots) that can be felt as noise that is extremely unpleasant to human hearing.
Consequently, aiming to reduce this unpleasant noise in the high-speed rotation region, configurations in which wedges are formed so as to have a general bucket shape, and entrance portions of the slots are blocked by stepped protruding portions at central portions of the wedges, or configurations in which protruding portions are made into an integrated resin molding shaped such that tip widths of the protruding portions have an interference relative to a width of the entrance portions of the slots to firmly fix them to the entrance portions of the slots are known. (See Patent Literature 1, for example.)
However, in such configurations, precision and accuracy must be ensured during production of the protruding portions of the wedges, and there have been problems such as a risk that the wedges may project beyond the inner peripheral surfaces of the stator and rub against the rotor if their height is incorrect, etc.
In answer to this, configurations are known in which the stepped portions on the inner periphery of the stator are made less likely to act as resonance tubes and unpleasant noise is reduced by forming irregular portions or penetrating apertures on or in surfaces of the wedges such that even if rarefaction and compression of the air occurs at the stepped portions when the rotor rotates at high speed inside the inner peripheral surfaces of the stator, the air is reflected diffusely by the irregular portions or penetrating apertures formed on or in the surfaces of the wedges. (See Patent Literature 2, for example.)
Patent Literature 1
                Japanese Patent Laid-Open No. SHO 60-170435 (Gazette)Patent Literature 2        Japanese Patent Laid-Open No. HEI 6-284618 (Gazette)        
However, in the configuration of Patent Literature 2, because the stepped portions still exist between the surfaces of the teeth and the inner peripheral surfaces of the wedges, and moreover the stepped portions exist so as to extend parallel to each other in an axial direction so as to be at a uniform pitch in a circumferential direction, one problem has been that the stepped portions still give rise to resonance effects, and are inclined to generate wind noise having components in orders dependent on the number of stator teeth (number of slots), and the frequencies of the unbalanced wind noise, being in a proportional relationship with the rotational frequency of the rotor as well as with the number of slots, are in frequency regions that are unpleasant to human hearing in the high-speed rotation region of the rotor.
Although conventionally the number of slots in alternators has been thirty-six, in recent years the number of slots has increased to seventy-two, ninety-six, etc., due to demand for compactness and high output, and one problem has been that unpleasant noise can now be sensed even when the rotor is at normal rotational speeds.